The invention relates to a deflecting device for electron beams, in particular for use in an electron beam vaporizer with a first magnetic deflecting unit having a central axis, where through the agency of said deflecting unit an electron beam entering the deflecting unit on the central axis experiences, due to a magnetic field system, a displacement parallel to the central axis in a displacement plane, where the intensity of the magnetic field system of the magnetic deflecting unit can be varied in order to determine the magnitude of the beam displacement, and with a second magnetic deflecting unit to steer the electron beam exiting the first magnetic deflecting unit out of the displacement plane.
A deflecting device of this type is described in connection with a vaporization system in DE 35 13 546 A1. The vaporization system comprises an elongated pot wherein it is achieved by means of varying beam displacement that the electron beam is traversed pendularly over longitudinal sections of the pot. Since the beam displacement is limited, in given cases several electron beam vaporizers, each with such a deflecting device, are provided next to one another in order to cover the entire length of the pot. Since the spatial exigencies of a vaporization system frequently do not permit guiding the electron beam directly into the pot, the displacement plane in which the beam displacement occurs is disposed above the pot and the electron beam is deflected directly above the pot from the displacement plane into the pot, i.e. onto the surface of the melt present there.
For this, a magnetic field is stretched along the pot, where the field lines of the magnetic field run parallel to the pot. So that the deflection occurs continuously in the same manner over the entire length of the pot the field must be made sufficiently homogeneous. However, it is difficult to realize such a homogeneous field by means of widely spaced armature plates of an electromagnet.
Furthermore, it should be possible to dispose the electron beam vaporizer under the passing substrates, where the high voltage used should not exceed 10 kV in order to avoid X-radiation.
The invention is therefore based on the object of providing a (second) deflecting unit in which the deflection from a displacement plane occurs, in so far as possible, in the same manner over the entire length of the pot.
To solve the problem the invention provides that the second magnetic deflecting unit generates a magnetic field running transverse to the central axis, the homogeneous area of said magnetic field being shorter than the maximum displacement which is to be achieved with the first deflecting unit, where the position of said magnetic field transverse to the central axis can be varied synchronously with the beam displacement.
A magnetic field whose length can be varied can be realized in that a plurality of air core coils is provided which are disposed next to one another on one axis. The individual air core coils are to be energized with current independently of one another so that on successive energizing of the coils with current the magnetic field moves from air core coil to air core coil.
However, a magnetic field generated by air core coils is not sufficiently intense to deflect the electron beam in the desired manner. On account of this a magnetic core is provided which is held displaceably on the axis. The magnetic core has approximately the length of one air core coil. It extends along the respective coil energized with current and in a known manner amplifies the magnetic field found therein.
Therefore, there is a sufficiently intense magnetic field in the area of the core, where this amplified field is spatially bounded. Since the air core coils are constructed identically, a magnetic field of the same type can therefore be established for deflecting an electron beam at any point in the air core coil system.
In the simplest case the coils are disposed next to one another on a guide tube and the core is guided within the guide tube, where its diameter corresponds approximately to the inner diameter of the guide tube. The core is preferably lubricated with a magnetic liquid.
Preferably, the guide tube is embodied with slots to avoid eddy currents in the longitudinal direction.
The air core coils are then each energized with current in mutually exclusive intervals of time or in given cases overlapping intervals of time, where the curve of the intensity of the current has a rising and falling shape, e.g. a saw-tooth or bell shape, so that it is always the case that a maximum current is supplied at least to precisely that air core coil over which the electron beam is presently located. If due to the control of the first deflecting unit the electron beam moves further in the longitudinal direction of the pot to the next air core coil, then with a corresponding control a magnetic field is generated in that air core coil so that the electron beam once again finds itself in a magnetic field which deflects it into the pot. The iron core follows the magnetic field moving through the air core coils and ensures in each case the necessary field intensity for redeflecting the electron beam. Thus it is achieved that the electron beam in the longitudinal direction of the pot can be wobbled back and forth over the melt and always strikes the material to be vaporized at the same angle of incidence.
The invention has the effect that through the synchronization of the first and second deflecting units the dwell times on the vaporant material and therefore the uniformity of coating is adjustable. Furthermore, the adjustment of the intensity of the magnetic field of the air core coils also permits a wobbling of the electron beam transverse to the longitudinal axis of the pot, whereby it is also possible to vaporize optical materials which sublimate in part.
The magnetic field system of the first deflecting unit, which causes the beam displacement, comprises preferably two tandemly disposed and antiparallelly aligned magnetic fields. Perpendicular to the magnetic field lines runs the displacement plane. Such devices are known per se. The electron beam enters the first magnetic field, in the displacement plane on the central axis lying in the displacement plane, and is, depending on the intensity of the magnetic field, deflected in the displacement plane by an angle to the left or to the right.
Since the second magnetic field runs antiparallel to the first magnetic field, the electron beam is steered back therein by the same angle so that all in all a parallel displacement of the electron beam is effected. Therefore a pendular displacement of the electron beam can be achieved, e.g. by a sinusoidal change of the excitation current of the electromagnets which generate the respective fields.
Customarily the magnetic fields in their projection onto the displacement plane are shaped rectangularly because this can be achieved by relatively simple, namely rectangularly shaped, armature plates for the electromagnets. The area of homogeneously running field lines is thus bounded by a rectangularly running magnetic field boundary. The disadvantage therein is that the electron beam exits the first magnetic field obliquely to the magnetic field boundary and likewise enters the second magnetic field obliquely. Thus scattering effects occur which expand the electron beam. It is thus proposed according to the invention that the magnetic field boundary of the first magnetic field has a convex contour on the exit side and the magnetic field boundary of the second magnetic field has a concave contour on the entry side.
The contour is chosen in so far as possible so that the electron beam at each point at which it exits the first magnetic field or enters the second magnetic field runs perpendicularly through the tangent at the magnetic field boundary. Scattering effects are avoided thereby so that the electron beam is expanded only slightly or not at all.
Such a magnetic deflecting unit which produces a beam displacement has magnetic fields that are each formed from two parallel-running armature plates of an electromagnet. In order to achieve the above-described contour of the magnetic field boundaries, the opposite edges of the armature plates have edges running parallel but curved.
The subject of the invention is also a device for vaporizing a planar substrate, e.g. a foil, with a thin material layer, in which the substrate is guided over an elongated pot so that the substrate is vaporized in each case over its width.
The coating of large-surface substrates, such as architectural glass, foils, etc. is done in general in so-called pass-through systems in which material is applied onto the substrate by a sputter process. The sputter sources are positioned under the substrates passing through as linear sources so that the substrates passing through can be coated from below. If, however, the coating is done using a commercial electron beam vaporizer with 270° beam deflection and in order to achieve better coating rates, then uniform coatings are, due to the geometry of the system, only to be achieved with great difficulty since for large substrate widths several electron beam vaporizers disposed next to one another must be used. Since these only strike the material pointwise, several apertures below the substrates and a large substrate spacing are necessary in order to achieve a uniform layer thickness distribution on the substrates. Because of the days-long operational period of such pass-through systems these apertures are vaporized so heavily that replacement of the apertures and therefore an interruption of the process would be necessary after a few hours. Thus previously known conventional electron beam vaporizers do not come into use for this application. In fact, commercial electron beam vaporizers are on the market which are directed obliquely from above onto the material to be vaporized. However, these electron beam vaporizers have the disadvantage that they are not suitable for pass-through systems since the electron beam gun would have to be disposed above the pot and therefore would be coated itself.
The material vaporization is done using an electron beam gun.
In order to obtain a compactly built device in which the material vaporization is done using an electron beam gun, the gun must be disposed below the transport path for the substrate and directed onto it. Disposition below the pot is still possible in given cases. For this a third deflecting unit deflects the electron beam directed onto the substrate approximately parallel to the transport path. Within this section of the electron beam, said section running parallel to the transport path, the above-described first deflecting unit is located in order to produce a varying beam displacement. Thereafter the electron beam is deflected into the pot using the third deflecting unit so that the electron beam strikes the melt surface perpendicularly in so far as possible.
The third deflecting unit can, as described above, comprise an axial sequence of air core coils in which a magnetic core can run back and forth. One air core coil row can be provided, preferably in the beam direction as seen from the pot, but also two or more air core coil rows can be provided, which preferably are disposed in front of and/or behind the pot. With such a double disposition of air core coil rows it can be achieved by a suitable control of the air core coils that the electron beam is wobbled in the beam direction, therefore not only longitudinally relative to the pot but rather is also deflected transversely relative thereto so that even for a wide pot the entire surface is traversed successively by the electron beam.
With the first deflecting unit, as already explained, a parallel displacement is produced so that the electron beam runs continuously perpendicular to the longitudinal extension of the pot. Since due to the explained shape of the second deflecting unit in the present area of the beam entry into the pot zone a sufficiently intense and consistently uniform magnetic field is generated, each electron beam is deflected into the pot in the same manner independently of its position in relation to the longitudinal extension of the pot. Therefore, a deflecting system is provided which is highly precise and enables uniform vaporization rates over the length of the pot.